1. Field of the Invention
The present invention relates to a notch position aligning mechanism in which the positions of notches formed in the edge portions of a plurality of targets to be aligned, such as semiconductor wafers, are aligned in a predetermined direction.
2. Description of the Related Art
IBM Technical Disclosure Bulletin Vol. 14, No. 8 issued in January 1972 discloses a technique in which semiconductor wafers (to be referred to as wafers hereinafter) serving as targets to be aligned having notches each having a radius of about 5 mm and formed in the edge portions of the wafers are stored in a cassette, and these semiconductor wafers are aligned in a predetermined state. According to this technique, a plurality of wafers stored in a cassette are lifted upward by a uniaxial roller having a diameter smaller than the diameter of the notch of each wafer, and the notches of the wafers are fitted on the roller by rotating the roller, thereby aligning the wafers.
However, when the wafers stored in the cassette are lifted upward by the uniaxial roller, the wafers cannot be supported by only the contact with the uniaxial roller. For this reason, the wafers are brought into contact with the wafer storing grooves of the cassette. In this state, when the roller is rotated, the wafers are rotated with the rotation of the roller, and the edge portions of the wafers are rubbed with the wafer storing grooves of the cassette with the rotation of the wafers. When the edge portions of the wafers are rubbed with the wafer storing grooves, a film formed on each wafer is peeled, or the wafers are damaged. As a result, dust generated by peeling of the films or damage to the wafers floats in the air, and this dust adheres to devices formed on each wafer, thereby decreasing the yield of the devices.
After the notches of the wafers are fitted on the uniaxial roller to align the wafers, the uniaxial roller cannot easily move the notches of the wafers to a predetermined position, e.g., a position which is located immediately above the roller and opposes the roller.